The present invention relates generally to barrel reactors and more particularly to apparatus for moving an exhaust tube of a barrel reactor between an operating position and a maintenance position.
Barrel reactors, such as generally indicated by the reference numeral 10 in FIG. 1, are used to deposit epitaxial layers on semiconductor wafers by a process known as chemical vapor deposition. The epitaxial layers have lattice structures which are identical to those of the wafers, but may be grown so they have different conductivity than the wafers to obtain necessary electrical properties. As illustrated in FIG. 2, the barrel reactor 10 comprises a reaction chamber 12 constructed from an inverted bell jar 14 for containing wafers W. A gas ring 30 sits atop an upper opening 16 of the bell jar 14. Nozzles 32 are provided in the gas ring 30 for introducing a reactant gas (e.g., silicon) into the reaction chamber 12. This gas forms the epitaxial layer on the wafers W contained in the chamber 12. After deposition is complete, the reactant gas is purged from the reaction chamber 12 through an exhaust tube, generally designated by 50' in FIG. 1, at the bottom of the bell jar 14. (Prime symbols are used with reference numbers herein to indicate that the designated component differs from the present invention.) The exhaust tube 50' includes an exhaust cup 52', flexible tubing 54 connected to the cup and rigid facility piping 56. Once purged, a seal plate 36 mounted on the gas ring 30 may be lifted to open the reaction chamber 12 to remove the wafers W from the barrel reactor 10.
Not only does material deposit on the wafers W contained in the reaction chamber 12, but it also deposits on the various components of the barrel reactor 10 during the chemical vapor deposition process. These deposits can become dislodged from the components and contaminate wafers during subsequent deposition operations. Consequently, the barrel reactor components must be replaced periodically to avoid contaminating wafers. Since the reactors 10 must be removed from service when the components are replaced, it is beneficial to reduce the time during which the reactors are out of service to reduce production costs associated with downtime.
In the past, apparatus such as that generally designated 150' in FIG. 1 has been used to move the exhaust tube 50', and more particularly the cup 52', between an operating position in which it is tightly sealed against an exhaust port 18 (FIG. 3) of the bell jar 14 and a maintenance position in which the exhaust tube is spaced from the exhaust port of the bell jar. Separating the exhaust cup 52' from the bell jar 14 permits the bell jar and/or portions of the exhaust tube to be replaced or serviced. The prior apparatus 150' comprises a cylinder, generally designated 90', positioned directly below the bell jar 14 and exhaust tube 50'. The cylinder 90' is connected to the exhaust tube 50' so that the exhaust tube seats against the bell jar exhaust port 18 when the cylinder is extended and separates from the exhaust port when the cylinder is retracted. As shown in FIG. 1, flexible tubing 54 is connected between the exhaust tube and facility exhaust piping 56 to permit the exhaust tube to move easily between the operating position and the maintenance position.
Prior apparatus 150' such as that described above are prone to failure due to the high temperature environment in which they are used. In particular, seals (not shown) in the cylinders 90' tend to fail when exposed to heat emitted by the bell jar 14 during chemical vapor deposition. Further, the prior exhaust cups 52' tend to fail in a region around their upper flanges 68'. This region has reduced material strength because the flange 68' is welded to the tube. Moreover, O-ring seals (not shown) used to seal the interface between the flange 68' and the bell jar 14 fail when exposed to high temperatures.